Molded products with a hinge structure are often used as resin molded products used for electrical and electric parts, automotive parts, and the like. With the increasing utilization of electronics in automobiles, electrical components in automobiles are increasing. In particular, as engine rooms are denser and a reduction in the size of electrical components is strongly requested, molded products with a hinge structure used in these components, such as relay blocks, connectors, and the like, have become more sophisticated and complicated in structure. Accordingly, there is demand for components with good hinge characteristics such that they will not break when bent repeatedly.
Conventionally, polyamide is known as a resin that can produce molded products with good hinge characteristics. However, since polyamide alone is not sufficient in terms of heat resistance, flame retardance, dimensional stability, mechanical strength, and so on, techniques have been examined for alloying polyamide with other resins to provide well-balanced characteristics. Representative alloy materials include polyamide/polyphenylene ether compositions. Polyphenylene ether is an amorphous resin and, in general, is not compatibilized with polyamide which is a crystalline resin. However, studies have been made of techniques for allowing polyphenylene ether to be compatibilized with polyamide by dispersing polyphenylene ether in polyamide using a compatibilizing agent.
To improve hinge characteristics in an alloy material of polyamide and polyphenylene ether, some methods have been proposed to increase the interface strength between polyamide and polyphenylene ether by increasing the molecular weight of polyamide or the amount of compatibilizer. Exemplary methods include a method to use a mixture of polyamide 6,6 and polyamide 6 as a polyamide with low viscosity (see, for example, PTL 1) and a method to increase moisture percentage (see, for example, PTL 2).